In a conventional image forming apparatus, a photosensitive drum transfers a latent image from the drum to a paper document or other image receiving medium. A fixing unit or device fixes the image to the paper by applying heat to the paper. The fixing unit is supplied with electric power to generate the necessary heat to fix the image to the paper. This supply of electric power to the fixing unit is limited because of electric power used by other components of the image forming apparatus. For example, the supply of electric power to the fixing unit is diminished when the image forming apparatus is scanning an original image or document because the scanning unit uses some of the available supply of electric power. As a general result, the supply of electric power to the fixing unit is relatively low during scanning, and relatively high at other times (i.e., when not scanning).
To fix the image properly to the document, the electric power supplied to the fixing unit must generate sufficient heat to produce a sufficient fixing temperature. The fixing temperature may be affected by environmental conditions, such as a cool environment, as well as operational conditions, such as a user performing continuous copying. Under various conditions, continuing the printing or copying for an extended period of time may result in the supplied electric power being insufficient to generate the necessary heat for proper fixing. This leads to defective fixing.
To prevent such defective fixing, the fixing unit typically enters into a “wait” operation during image forming, which generally means that the actual printing waits for the necessary temperature rise/recovery in the fixing device. When the fixing unit goes into the wait operation, printing or copying operations are temporarily stopped, pending recovery of the fixing temperature of the fixing device. Such interruptions to copying and printing operations are disruptive to all users of the image forming apparatus.